Expansible drill collar stabilizer



Aug. 25, 1964 J. M. KELLNER EXPANSIBLE DRILL CQLLAR STABILIZER 4Sheets-Sheet 1 Filed Feb. 15, 1960 Inventor Jackson M. Kellner B %.-w02. LL Attorney Aug. 25, 1964 J. M. KELLNER 3,145,785

EXPANSIBLE DRILL COLLAR STABILIZER Filed Feb. 15, 1960 4 Sheets-Sheet 2FIG. IA FIG. 3A

Jackson M. Kellner INVENTOR.

BY 2...) z. Q4. ATTORNEY Aug. 25, 1964 J. M. KELLNER EXPANSIBLE DRILLCOLLAR STABILIZER 4 Sheets-Sheet 3 Filed Feb. 15, 1960 Ill FIG.

Inventor Jackson M. Kellner By a. Q....L Attorney Aug. 25, 1964 J. M.KELLNER EXPANSIBLE DRILL COLLAR STABILIZER 4 Sheets-Sheet 4 Filed Feb.15. 1960 FIG. 5

Inventor 4 Jackson M. Kellner By 2%...) 2. Q)... Attorney United StatesPatent 3,145,785 EXPANSIBLE DRILL COLLAR STABILIZER Jackson M. Kelluer,Tulsa, Gkla, assignor to Jersey Production Research Company, acorporation of Delaware Filed Feb. 15, 1%0, Ser. No. 8,789 16 Claims.(Cl. 175-73) The present invention relates to apparatus useful fordrilling boreholes in the earth and more particularly relates to animproved drill collar stabilizer for straightening crooked boreholesduring rotary drilling operations. In still greater particularity, theinvention relates to a drill collar stabilizer provided with atelescoping structure which permits expansion of the stabilzer ribswithin the borehole.

It is conventional during the rotary drilling of oil wells, gas wellsand similar boreholes in the earth to employ a series of heavy drillcollars near the lower end of the rotary drill string in order tomaintain high pressures between the drill bit and the formation beneaththe bit and at the same time keep the relatively thin walled drill pipein the upper part of the borehole in tension. This prevents buckling andflexing of the pipe and greatly increases the drilling effectiveness ofthe bit. The drill collars thus employed are normally positioned justabove the bit and may extend several hundred feet up the drill string.Because they are under compression, the collars themselves tend tobuckle, however, even though the drill pipe does not. This bucklingaction, coupled with the tendency of dipping, laminated strata todeflect the bit, often leads to the drilling of crooked, slopingboreholes. In such a borehole, the weight of the drill collars below thepoint of last contact with the borehole wall may be divided into twocomponents: one acting along the axis of the collars and a second actingnormal to the first toward the low side of the borehole. This secondcomponent is usually referred to as the pendulum force. The portion ofthe drill string above the point of last contact which is undercompression results in an additional force which is transmitted axiallyby the drill collars to the bit and is in effect applied from the pointof last contact at an angle to the vertical greater than the deviationangle. Ignoring effects due to the heterogeneity of the formation beingdrilled, the bit will advance in the direction of the resultant of thependulum force and the forces transmitted axially to the bit by thedrill collars. If the angle of this resultant to the vertical exceedsthe deviation angle, continued drilling will result in an increase indeviation; whereas a decrease in deviation will occur with continueddrilling if the angle of the resultant is less than the deviation angle.The angle which the resultant makes with the vertical can be reduced bychanging the pendulum force, by changing the forces transmitted axiallyto the bit by the drill collars, or by changing the direction in whichthe axially-transmitted forces are applied to the bit.

The method generally employed for correcting deviation during a rotarydrilling operation is to place a drill collar stabilizer in the drillstring at a point some distance above the bit in order to hold the drillcollars away from the borehole wall. This raises the point of contactbetween the drill string and wall and thus increases the magnitude ofthe pendulum force acting on the bit. It also decreases the angle to thevertical at which the forces transmitted axially by the drill collarsare applied to the bit. The point at which the stabilizer should beplaced for maximum effectiveness depends upon the angle of inclinationof the borehole, the diameter of the borehole and drill collar, theweight on the bit, and the type of formation being drilled. Generallythe distance between the stabilizer and bit ranges from about 30 toabout 100 feet. The change in the forces acting on the bit when3,145,785 Patented Aug. 25, 1964 the stabilizer is placed at the properpoint counteracts the forces responsible for deviation of the borehole.

The conventional drill collar stabilizer employed for the purposedescribed above is generally a tubular sub provided with lateralprojections or ribs which, when the stabilizer is connected betweenadjacent drill collars, will bear on the sloping borehole wall and holdthe collars away from the wall. The outer diameter of the ribs of such astabilizer must be slightly smaller than the diameter of the borehole inorder to permit continuou downward movement of the drill string as thedrilling operation progresses. The outer diameter should be as large aspossible, on the other hand, so that the drill collars can be held amaximum distance away from the borehole wall. Stabilizers employedheretofore have generally had fixed projections or ribs made of rubber,steel or similar mate rial. Experience has shown that stabilizers ofthis type are not wholly satisfactory because the projections or ribstend to scrape against and snag the Walls of the borehole during tripsto and from the surface. This often results in damage to the boreholewall and in some cases may cause the drill string to become stuck in theborehole. In addition, shales tend to accumulate on the projecting ribsas the stabilizer is pulled out of the hole and as a result the ribs arefrequently torn or badly worn.

The use of drill collar stabilizers provided with ribs or projectionswhich will deflect upon contact with the borehole wall during trips intoand out of the borehole has recently been suggested as a means forovercoming the difliculties encountered with conventional stabilizershaving fixed ribs. It is diflicult to make the projections on such astabilizer resilient enough to avoid damage to the borehole wall duringtrips into and out of the borehole and yet make them stiif enough toresist the weight of the drill collars against the wall of the slopingborehole. Moreover, problems due to the accumulation of shales whichtend to tear and abrade the ribs during trips into and out of theborehole are encountered despite the resiliency of the ribs.

The present invention provides a new and improved drill collarstabilizer which avoids the difiiculties encountered with stabilizersavailable heretofore and thus makes the use of stabilizers moreattractive for use in a variety of drilling operations where boreholedeviations may be encountered. In accordance with the invention. theimproved stabilizer thus provided utilizes a telescoping sub providedwith elastic ribs which may be expanded or contracted in response to themotion of the sub. The weight of the drill collars below the sub isemployed to hold the ribs in a retracted position during trips into theborehole. When this weight is taken up as the bit reaches the bottom ofthe hole and bears against the formation, the ribs are expanded andsupport the drill collars away from the borehole wall. Raising the drillstring to withdraw it from the hole again retracts the ribs. Theoperation of the stabilizer is thus fully automatic and does not requireback rotation of the drill string or similar manipulation. It has beenfound that the improved stabilizer permits rapid tripping into and outof the borehole, reduces stabilizer damage due to wear and abrasionduring such tripping, and greatly decreases the likelihood of damage tothe borehole wall.

The exact nature and objects of the invention can best be understood byreferring to the following detailed description of several embodimentsof the improved drill collar stabilizer and to the accompanyingdrawings, in which:

FIG. 1 is a partially-sectioned vertical view of one embodiment of thestabilizer of the invention utilizing resilient ribs mounted on thestabilizer sub so that the ribs are expanded as the effective length ofthe sub is reduced;

FIG. 1A is a fragmentary view showing in greater detail the splines orkeys on the apparatus of FIG. 1;

FIG. 2 is a cross-sectional view of the stabilizer shown in FIG. 1 takenabout the line 22;

FIG. 3 is a partially-sectioned vertical view of a stabilizer similar tothat shown in FIG. 1 but provided with a hearing which reduces thenecessity for lubricating the apparatus;

FIG. 3A is an enlarged view of the bearing sleeve utilized in theapparatus of FIG. 3;

FIG. 4 is a partially-sectioned vertical view of a further embodiment ofthe stabilizer of the invention which utilizes resilient ribs molded toexpanded size, and

FIG. 5 is a cross-sectional view through the stabilizer of FIG. 4 takenabout the line 5-5.

Referring first to FIG. 1 of the drawings, it will be seen that thestabilizer depicted therein includes a generally tubular mandrel 11which has three distinct but integral sections. At the upper end of themandrel is a piston section 12 of enlarged outer diameter upon which aremounted wiper and seal ring 13 and wiper ring 14. The rings may be madeof rubber, plastic, hemp or similar material resistant to oil, water andother fluids which may be encountered or employed during rotary drillingoperations. They are set in annular grooves in the outer surface of thepiston and will normally be retained therein by their own elasticity. Insome cases, however, non-resilient materials may be used for sealingpurposes, in which event suitable retainer rings may be provided. Piston12 is separated from the lower portion of mandrel 11 by an annular,downwardly facing shoulder 15.

Immediately below the piston section of the mandrel is an intermediatesection 16 having a substantially uniform outer diameter somewhatsmaller than the outer diameter of the piston.

Keys or splines 17 are positioned on the outer surface of intermediatesection 16 near the upper end thereof and serve to transfer torque tothe mandrel. The splines extend parallel to the longitudinal axis of themandrel and are preferably spaced at intervals about the entire surfaceof the intermediate section. At the lower end of intermediate section 16is tapered shoulder 18 which serves to seat the mandrel in an annularsleeve to be described hereafter.

Below tapered shoulder 18 on mandrel 11 is lower section 19 which has anouter diameter somewhat less than that of the intermediate section. Thelower end of section 19 is provided with threads 20 for connecting themandrel to a collar 21 fitted with a standard API tool joint pin 22. Theupper rim of the collar surrounding the mandrel is provided withserrations 23 which, as will be explained hereafter, serve to restrictrelative motion between the various parts of the stabilizer duringwashover operations. The mandrel contains an axial passage 24 for thecirculation of fluids through the stabilizer.

The stabilizer assembly shown in FIG. 1 of the drawings is also providedwith a supporting structure which includes an upper housing 26 intowhich the upper end of mandrel 11 extends. At the upper end of thehousing is a standard API tool joint box 27 by means of which thestabilizer may be connected to a conventional drill collar or section ofdrill pipe. Below box 27 the internal diameter of the housing isenlarged to form shoulder 28 and cylinder 29. Piston 12 on the mandrel,including wiper and seal ring 13 and wiper ring 14, extends into thecylinder and is free to move axially with respect to the housing. Thelower part of the housing is provided with internal threads 30.

Connected to housing 26 by means of threads 30 is an intermediatesection of the supporting structure, splined sleeve 31 which containssplines 32. The splines mate with those on the mandrel 11 and provide ameans for transferring torque from the housing and sleeve to themandrel. The length of the splines on sleeve 31 is sufficient to permitaxial movement of the piston section of the mandrel within the limits ofcylinder 29. The splines are shown in greater detail in FIGURE 1A of thedrawing.

Tapered sleeve 33 at the lower end of the supporting structure isconnected to the lower end of splined sleeve 31 by means of threads 34.The internal diameter of the upper part of the tapered sleevecorresponds to that of the lower section of the splined sleeve. At anintermediate point on the tapered sleeve is internal shoulder 35, belowwhich the inside diameter of the sleeve is reduced. The lower, outeredge of sleeve 33 is tapered as indicated by reference numeral 36.

Elastic sleeve 37 is supported on the intermediate section 16 of mandrel11 and extends over the lower part of tapered sleeve 33 surrounding themandrel. The elastic sleeve may be made of natural or synthetic rubberor similar elastic material and may be provided with reinforcing threadsor filaments of nylon, rayon or the like.

Chloroprene and nitrile type synthetic rubbers are preferred because oftheir high resistance to deterioration in the presence of oils. Ribs 38are molded or otherwise formed on the outer surface of the sleeve atspaced points about its circumference. The sleeve and rib configurationis shown more clearly in FIG. 2 of the drawings. At its lower end theelastic sleeve is connected to a lower sleeve 39 provided with aninternal shoulder 40 corresponding to shoulder 18 on mandrel 11. Theelastic sleeve and lower sleeve 39 may be interlocked as shown in FIG. 1or may be connected by bands and rivets or the like. In some cases thesleeves may be bonded or cemented together. The lower edge of sleeve 39is provided with serrations 41 which mate with serrations 23 on collar21. The faces of the serrations on the collar and sleeve should beinclined so that the collar can rotate in a clockwise directionindependently of the sleeve but will turn the sleeve when rotatedcounterclockwise.

In using the embodiment of the invention shown in FIG. 1 of thedrawings, the stabilizer is generally inserted in the drill collarsection of the rotary drill string at a point ranging from about 30 toabout feet above the bit. The most effective distance will depend upon anumber of factors, including the type of formation being drilled, theinclination of the borehole, the diameter of the bit and drill collars,and the weight to be used on the bit. It is generally preferred tosurvey the borehole just before the drill string is withdrawn, using aninclinometer or similar instrument, and then employ tables developed forthat purpose to select the stabilizer position. Standard tables givingoptimum stabilizer locations for various conditions have been publishedand will be familiar to those skilled in the art. After the stabilizerhas been inserted at the proper place in the drill string, the string islowered into the borehole.

During trips into and out of the borehole, the stabilizer is supportedby the upper part of the drill string attached to housing 26. The weightof the drill collars and bit below the stabilizer hold mandrel 11 in adownward position in cylinder 29 so that shoulder 15 on the mandrelrests upon the upper edge of splined sleeve 31. The stabilizer ribs 38remain in the retracted position shown in FIGS. 1 and 2 of the drawings.When the bit reaches the bottom of the hole, the weight of the mandrel,lower drill collars, and bit is transferred from housing 26 to theformation. This prevents further movement of the mandrel in a downwarddirection. Housing 26, splined sleeve 31 and tapered sleeve 33 continueto move downward, however, due to the weight of the drill collars abovethe stabilizer. The tapered end 36 of sleeve 33 is forced downwardlybeneath elastic sleeve 37, moving rib 38 on the sleeve outwardly into anexpanded position. The elastic sleeve is attached to sleeve 39 whichbears against collar 21 on the mandrel and hence cannot move with thetapered sleeve. Downward movement of the housing and associated sleevethus continues until shoulder 28 in the housing rests upon the top ofpiston 12 on the manin the art.

to the drill collars and bit below by splines 32 on the splined sleeveand matching'spline 17 on the mandrel. The outer diameter of theexpanded stabilizer ribs is slightly less than the diameter of the bitand hence the stabilizer is free to slide along the walls of theborehole as the bit advances. Due to the absence of high contactpressures between the ribs and the wall of the hole and the force on thebit. This also reduces the angle to the vertical at which forces aretransmitted axially by the drill collars to the bit. As a result, thebit tends to drill in a more vertical direction. The stabilizer thuscorrects or controls the deviation of the borehole. More weight can beapplied to the bit to increase drilling effectiveness than could beif astabilizer were not used.

The stabilizer ribs 38 can readily be retracted to permit withdrawal ofthe drill string from the borehole. Raising the string from the surfacecauses housing 26 and sleeves 31 and 33 to move upwardly with respect tothe mandrel 11 in elastic sleeve 37. The lower edge of the taperedsleeve 33 is pulled upwardly with respect to the elastic sleeve. and theribs are retracted. Thereafter, shoulder 15 engages the upper end ofsleeve 31 and the entire stabilizer moves as a unit. Retraction of theribs in this manner permits tripping without danger of damaging theborehole wall or injuring the stabilizer ribs. The likeli- -hood of thestabilizer becoming stuck in the borehole during tripping is greatlyreduced.

In the event that the stabilizer should become stuck in the borehole,however, it can be removed by lowering a conventional washover tool overthe drill string and milling off the ribs projecting from the surface tothe stabilizer. A variety of washover tools suitable for this purposeare available and will be familiar to those skilled Rotation of theelastic sleeve on the mandrel during such a washover operation isprevented by serra- 'tions 23 on collar 21 and matching serrations 41 onlower sleeve 39. The serrations lock together and prevent clockwiserotation of the sleeve with respect to the mandrel but do not interferewith the normal rotation of the mandrel within the sleeve duringdrilling. The elastic sleeve must be replaced following such a washoveroperation but other parts of the stabilizer are normally not damaged.This minimizes the cost of the washover operation and makes the use ofthe improved stabilizer considerably more attractive from an economicstandpoint than the use of stabilizers having fixed, integral ribs.

The ribs on the stabilizer shown in FIGS. 1 and 2 of the drawing tend torotate with the tool because of friction between the tapered sleeve andthe elastic sleeve, although this tendency can be reduced somewhat bythe use of a lubricant between the two sleeves. The embodiment shown inFIG. 3 diifers from the earlier embodiment in that such rotation doesnot occur.

The stabilizer depicted in FIG. 3 is generally similar to that shown inFIGS. 1 and 2 but employs a bearing in the supporting structure to avoidfriction between the tapered sleeve and the elastic sleeve. Mandrel 111in FIG. 3 contains at its upper end piston section 112 upon which aremounted seal and wiper ring 113 and wiper ring 114. Intermediate mandrelsection 115 below the piston section has an outer diameter somewhat lessthan that of the piston section. Splines 116 are located on theintermediate section near the upper end thereof. Lower man- 137 aremolded integral with the elastic sleeve.

collar permits the circulation of drilling fluid through the stabilizer.

Cylindrical housing 124 at the upper end of the supporting structureonthe stabilizer contains an API tool joint box 125 which communicateswith a cylinder below shoulder 126 into which the piston section 112 ofmandrel 111 extends. Splines 127 on the inner wall of the housing matewith splines 116 on the mandrel and permit the transmission of torque.Connecting sleeve 128 of the supporting structure into which splines 127extend is attached to the lower end of the housing by means of threads129. The connecting sleeve is in turn connected by threads 130 tobearing support 131 of the supporting structure. The bearing supportcontains an annular shoulder 132 which serves as the bearing surface.

Bearing sleeve 133 of the supporting structure, shown in greater detailin FIGURE 3A of the drawing, which may be made of brass, steel, rubber,or similar material, is retained on the bearing support over shoulder132 and is free to rotate thereon. The bearing sleeve contains internallands 133a provided with shoulders 133b which bear against the uppersurface of shoulder 132 as the bearing sleeve turns with respect to thebearing support 131. Windows 1330 permit fluid to circulate between thelands to prevent the accumulation of solids in the sleeve. Taperedsleeve 134 at the lower end of the supporting structure is connected tothe lower end of the bearing sleeve by threads 135. Elastic sleeve 136is supported on the intermediate section of the mandrel and extendsupwardly over the lower end of the tapered sleeve. Ribs Lower sleeve 138is attached to the lower end of the elastic sleeve and contains aninternal shoulder 139 which matches shoulder 118 on the mandrel.Serrations 140 are provided on the lower sleeve for locking the sleeveand collar 120 for counterclockwise rotation. The collar and mandrel arefree to rotate in clockwise direction independently of the sleeve.

Operation of the stabilizer of FIG. 3 is similar to that of theembodiment depicted in FIGS. 1 and 2. The ribs 137 are expandedoutwardly into the position shown in FIG. 3 by downward movement oftapered sleeve 134 beneath elastic sleeve 136. The bearinginterconnecting the tapered sleeve and the upper assembly permits thetapered sleeve to remain stationary as the drill string is rotated andhence reduces friction on the elastic sleeve. Because of this reducedfriction, lubrication of the stabilizer is unnecessary.

The embodiment of the invention shown in FIGS. 4 and 5 of the drawingsdiffers somewhat from the earlier described embodiments in that thestabilizer ribs are molded to full or expanded size on the stabilizersub and are retracted for tripping purposes in response to tension fromthe elastic sleeve.

Referring to FIG. 4, reference numeral 211 designates a stabilizermandrel which contains an upper piston section 212 bearing wiper ring213 and seal ring 214. Below the piston section, intermediate mandrelsection 215 of reduced diameter carries splines 216 on the outer surfacethereof. Lower mandrel section 217 is separated from the intermediatesection by tapered shoulder 218. Threads 219 connect the mandrel to acollar 220 bearing an API tool joint pin 221 at its lower end.Serrations 222 are located on the upper rim of the collar for use duringwashover operations. Mandrel bore 223 permits the circulation of fluidsthrough the apparatus.

Housing 224 of the supporting structure at the upper end of thestabilizer assembly contains API tool joint box 225 and bore 226 whichcommunicates with the bore of mandrel 211. Tapered sleeve 227 at thelower and of the supporting structure is connected to the lower end ofthe housing by threads 228. The sleeve is provided with splines 229 thatmate with those on the mandrel, the

latter being axially slidable in the sleeve. The outer diameter of thesleeve is reduced below an annular shoulder 230 located at anintermeidate point thereon. A secon shoulder 231 below shoulder 230separates the intermediate section of the sleeve from a lower section ofslightly larger outside diameter. The lower skirt of sleeve 227 istapered toward the mandrel as indicated by reference numeral 232.

Upper sleeve 233 is positioned on tapered sleeve 227 between shoulders230 and 231 and is free to rotate and move axially thereon. Near itslower edge, sleeve 233 contains an integral shoulder 234 which engagesshoulder 231 on sleeve 227 and restricts its downward movement. Elasticsleeve 235 of rubber or similar material is connected to the lower endof annular sleeve 233 and extends downwardly over tapered sleeve 227below shoulder 231. Ribs 236 are molded into the elastic sleeve aboutsolid inserts 237 spaced around the periphery of the stabilizer. Theribs are molded to the full or expanded size and are not bonded to theinserts. The cross-sectional area of the sleeve, including the ribs,should be essentially uniform over its length. FIG. 5 of the drawingshows the ribs and inserts in cross section. Lower sleeve 238 isattached to the lower edge of the elastic sleeve and is provided with aninternal shoulder 239 which may seat against shoulder 218 on themandrel. The lower edge of sleeve 238 contains serrations 240 which matewith those on collar 220 to permit clockwise rotation of the mandrel andcollar independently of the elastic sleeve and upper and lower sleevesattached thereto and yet prevent independent rotation during washoveroperations. Resilient skirt 241 is positioned at the lower outer edge ofsleeve 238 and bears upon the upper surface of collar 220 to preventengagement of the serrations on the collar and sleeve in the absence ofa downward force on the sleeve.

During trips into and out of the borehole with the stabilizer shown inFIGS. 4 and 5 of the drawings, the weight of the drill collars and bitbelow the stabilizer holds mandrel 211 in a downward position within theassembly. Shoulder 218 on the mandrel seats against shoulder 239 onlower sleeve 238 and hence the elastic sleeve is pulled downwardly withthe mandrel. Ribs 236 and solid inserts 237 are held below the loweredge of tapered sleeve 227. Shoulder 231 on the tapered sleeve engagesshoulder 234 on upper sleeve 233 and thus an upward force is exerted onthe elastic sleeve. The

resulting elongation of the sleeve due to the tension reduces the ribsto the retracted diameter. Because of the uniform cross section of theelastic sleeve, the elongation is substantially uniform over its length.Since the inserts are not bonded to the sleeve, they do not interferewith elongation. With the ribs thus retracted, there is little danger ofdamage to the ribs or borehole walls and little opportunity for thestabilizer to become stuck in the borehole during tripping.

The stabilizer ribs are automatically expanded when the drill stringreaches the bottom of the borehole. The weight of the string above thestabilizer causes the housing and tapered sleeve to move downwardlyaround the mandrel. This reduces the tension on the elastic sleeve sothat the ribs can expand outwardly into their normal position. Thetapered sleeve moves down beneath the elastic sleeve and ribs to supportthem. The rib inserts provide lateral strength to resist the contactpressure between the ribs and the borehole wall. In this expandedposition, the elastic sleeve is not under radial tension and hence themandrel and tapered sleeve can rotate within the sleeve without buildingup high friction forces. This reduces the lubrication requirements ofthe stabilizer and provides a more dependable tool than can otherwise beobtained.

It will be recognized that other modifications of the stabilizer of theinvention can be made without departing from the scope of the invention.The ribs on the stabilizer depicted in FIGS. 1 and 2 of the drawings,for example, can be molded to expanded size. In this case, the ribswould not be retracted when the stabilizer sub is in the extendedposition shown in FIG. 1 of the drawings but would nevertheless be freeto move inwardly in response to light radial loads such as might beencountered when passing a bridged section of the borehole duringtripping. Movement of the tapered sleeve beneath the elastic sleevewould support the stabilizer ribs when the stabilizer is in use withoutrequiring that the sleeve be in radial tension. This would reduce thefriction between the elastic sleeve and tapered sleeve and avoid theproblem of lubricating the sleeves.

What is claimed is:

1. A drill collar stabilizer comprising a tubular supporting structurehaving a tapered lower edge; a tubular mandrel having one end slidablypositioned within said supporting structure and extending therefrombelow said tapered edge in telescopic relationship to said supportingstructure; means for limiting axial movement of said mandrel withrespect to said supporting structure; an elastic sleeve havingcircumferentially-spaced ribs on the outer surface thereof, said elasticsleeve being rotatably mounted on said mandrel and extending upwardlyover said tapered edge; means for limiting axial movement of saidelastic sleeve with respect to said mandrel; and means for transmittingtorque between said mandrel and said supporting structure.

2. A stabilizer as defined by claim 1 wherein said supporting structureincludes an upper assembly, a lower sleeve, and a bearing sectioninterconnecting said upper assembly and said lower sleeve.

3. A stabilizer as defined by claim 1 wherein rotatable upper and lowersleeves are mounted on said supporting structure and mandrelrespectively and the upper and lower ends of said elastic sleeve areattached to said upper and lower sleeves respectively.

4. A stabilizer as defined by claim 1 wherein the normal inside diameterof the upper part of said elastic sleeve is greater than the outsidediameter of the portion of said supporting structure over which saidelastic sleeve extends.

5. A stabilizer as defined by claim 1 wherein rib inserts are positionedbeneath said elastic sleeve and are supported by said supportingstructure over which said elastic sleeve extends.

6. A drill collar stabilizer comprising a tubular supporting structureprovided at the upper end thereof with means for connecting saidsupporting structure to a rotary drill string, said structure having atapered lower edge; a tubular mandrel axially slidable within saidsupporting structure and extending below said tapered edge in telescopicrelationship to said supporting structure, said mandrel including meansfor connecting the same to a rotary drill string below the mandrel;means interconnecting said mandrel and said supporting structure for thetransfer of torque from said supporting structure to said mandrel; meansfor limiting axial movement of said mandrel with respect to saidsupporting structure; an elastic sleeve having integral ribscircumferentially spaced and extending longitudinally on the outersurface thereof, said elastic sleeve being rotatably mounted on saidmandrel below said supporting structure and extending above the taperededge thereof and said mandrel including means for limiting axialmovement of said sleeve thereon; and means for limiting rotation of saidelastic sleeve on said mandrel.

7. A stabilizer as defined by claim 6 wherein said means for limitingrotation of said elastic sleeve includes a rotatable sleeve mounted onsaid mandrel and provided with serrations which engage mating serrationson said mandrel and the lower end of said elastic sleeve is connected tosaid rotatable sleeve.

8. A stabilizer as defined by claim 6 wherein said tubular supportingstructure includes a tubular upper assembly, a lower sleeve, and anannular bearing sleeve which is attached to said lower sleeve androtatable on said upper assembly.

9. A stabilizer as defined by claim 6 wherein the normal inside diameterof said elastic sleeve is sufliciently large to permit rotation of saidmandrel and the lower portion of said supporting structure therebeneathwithout radial tension in said sleeve.

10. A stabilizer as defined by claim 6 wherein a rotatable sleeve ismounted on said supporting structure above said tapered edge and isattached to the upper end of said elastic sleeve and means are providedfor limiting axial movement of said rotatable sleeve on said supportingstructure.

11. A drill collar stabilizer comprising a tubular supporting structureadapted at the upper end to be connected to a rotary drill string andhaving an elongated section of reduced outer diameter at the lower end,said supporting structure including internal splines; a tubular mandrelhaving external splines mating with said internal splines, said mandrelbeing axially slidable in said supporting structure and extendingtherefrom below said elongated section and including means forconnecting the same to a rotary drill string below the mandrel and saidsupporting structure including means for limiting axial movement of saidmandrel; a rotatable upper sleeve externally mounted and axiallyslidable on said elongated section of said supporting structure, saidsupporting structure including means for limiting axial movement of saidupper sleeve; a rotatable lower sleeve externally mounted and axiallyslidable on said mandrel below said supporting structure, said mandrelincluding means for limiting axial movement of said lower sleeve; and anelastic sleeve rotatable over said mandrel and said elongated section ofsaid supporting structure connected at one end to said upper sleeve andat the other end to said lower sleeve, said elastic sleeve havingcircumferentially-spaced external ribs beneath which said elongatedsection of said supporting structure extends when said mandrel is in anupper position with respect to said supporting structure and which arebelow said elongated section when said mandrel is in a lower positionwith respect to said supporting structure.

12. A stabilizer as defined by claim 11 including rigid rib inserts overwhich said ribs on said elastic sleeve extend.

13. A stabilizer as defined by claim 11 wherein said lower sleevecontains serrations on the lower edge thereof and said mandrel includesan upperwardly facing shoulder containing matching serrations, saidserrations being adapted to prevent clockwise rotation of said lowersleeve on said mandrel when said lower sleeve is in the lowermostposition thereon.

14. A drill collar stabilizer comprising a tubular upper assemblyadapted at the upper end to be connected to a rotary drill string andhaving a section of reduced external diameter at the lower end, saidupper assembly containing internal splines and said section of reduceddiameter including an upwardly facing shoulder located near the lowerend thereof; a tubular mandrel having external splines mating with saidinternal splines, said mandrel being axially slidable in said upperassembly and extending therefrom below said section of reduced externaldiameter, said upper assembly including means for limiting axialmovement of said mandrel therein, and said mandrel including means nearthe lower end thereof for connecting the same to a drill string; anannular sleeve having an internal downwardly facing shoulder rotatablymounted on said section of reduced diameter on said upper assembly, saidshoulder on said sleeve bearing against said shoulder on said section ofreduced external diameter; an elongated sleeve rotatably mounted andaxially slidable on said mandrel below said upper assembly, saidelongated sleeve being connected to said annular sleeve on said upperassembly; a rotatable lower sleeve mounted and axially slidable on saidmandrel below said elongated sleeve, said mandrel including means forlimiting axial movement of said lower sleeve thereon; and an elasticsleeve rotatably mounted on said mandrel and extending upwardly oversaid elongated sleeve, said elastic sleeve being connected to said lowersleeve and having circumferentially-spaced external ribs beneath whichsaid elongated sleeve extends when said mandrel is in an upper positionwith respect to said upper assembly and which are below said elongatedsleeve when said mandrel is in a lower position with respect to saidupper assembly.

15. A stabilizer as defined by claim 14 wherein said annular sleevecontains internal longitudinal grooves through which fluid may circulatebetween said sleeve and housing.

16. A drill collar stabilizer comprising a tubular upper assemblyadapted at the upper end to be connected to a rotary drill string andhaving an elongated section of re duced external diameter at the lowerend, said upper assembly having internal splines; a tubular mandrelhaving external splines mating with said internal splines in said upperassembly, said mandrel being axially slidable in said upper assembly andextending therefrom below said section of reduced external diameter,said upper assembly including means for limiting axial movement of saidmandrel therein and said mandrel including means for connecting the sameto a drill string below the mandrel; a rotatable sleeve mounted andaxially slidable on said mandrel below said elongated section of reducedexternal diameter on said upper assembly, said mandrel including meansfor limiting axial movement of said rotatable sleeve thereon; and anelastic sleeve rotatably mounted on said mandrel and extending upwardlyover said elongated section of reduced diameter on said upper assembly,said elastic sleeve being connected to said rigid sleeve and havingcircumferentially-spaced external ribs beneath which said elongatedsection of reduced diameter extends when said mandrel is in an upperposition with respect to said upper assembly and which are below saidelongated section of reduced diameter when said mandrel is in a lowerposition with respect to said upper assembly.

References Cited in the file of this patent UNITED STATES PATENTS1,692,181 Machris Nov. 20, 1928 2,052,786 Meyer Sept. 1, 1936 2,173,309Monroe Sept. 19, 1939 2,589,534 Buttolph Mar. 18, 1952 2,876,992 LindsayMar. 10, 1959 2,891,769 Page et a1. June 23, 1959

1. A DRILL COLLAR STABILIZER COMPRISING A TUBULAR SUPPORTING STRUCTUREHAVING A TAPERED LOWER EDGE; A TUBULAR MANDREL HAVING ONE END SLIDABLYPOSITIONED WITHIN SAID SUPPORTING STRUCTURE AND EXTENDING THEREFROMBELOW SAID TAPERED EDGE IN TELESCOPIC RELATIONSHIP TO SAID SUPPORTINGSTRUCTURE; MEANS FOR LIMITING AXIAL MOVEMENT OF SAID MANDREL WITHRESPECT TO SAID SUPPORTING STRUCTURE; AN ELASTIC SLEEVE HAVINGCIRCUMFERENTIALLY-SPACED RIBS ON THE OUTER SURFACE THEREOF, SAID ELASTICSLEEVE BEING ROTATABLY MOUNTED ON SAID MANDREL AND EXTENDING UPWARDLYOVER SAID TAPERED EDGE; MEANS FOR LIMITING AXIAL MOVEMENT OF SAIDELASTIC SLEEVE WITH RESPECT TO SAID MANDREL; AND MEANS FOR TRANSMITTINGTORQUE BETWEEN SAID MANDREL AND SAID SUPPORTING STRUCTURE.